I was doing some testing for a upcoming project attempting to router a slot into some plywood. I set the 1/4 straight flute bit to roughly 1/4 deep, plunged the plywood onto the bit and routed roughly 1 1/2” slot. When I removed the plywood, there was a bit of blackness on the slot and the end of the bit that was in the wood was black.
Was I feeding too slow, too fast or do I need a spiral bit to really make this work?

Thanks in advance!

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25 replies so far

sounds rather normal. 1/4” slot is narrow – not a whole lot of air and space for chips to clear and heat to dissipate adding to the already susspeceptive to burn process (router at high speed). plunging also adds a great deal of probability to burning. a spiral bit would help in 2 ways:

spiral channels will clear chips more efficiently

acts more like a drill for plunging actions than a straight bit

with that said, 1/4” deep is fairly deep… I would recommend lowering the depth to 1/8” or even less depending on your wood/bit/experience and doing this in 2-3 passes each pass taking a bit of depth until the final pass which gets you to the desired depth. this would reduce/eliminate burning, as well as protect your bits./routermotor long term

The plywood being laminated sheets have a lot of glue in them. A steel flute bit or any other steel bit will more likely turn black with plywood and oily woods. Look for a carbide bit to eliminate the problem. more expensive but worth it.

Normal. I don’t think you can normally burn carbidewith normal woodworking applications, but oilsand glues seem to liquify at router speeds and contribute to burning. A bit can get hot enough from cutting wood to burn the wood pretty easily too.

Oven cleaner removes pitch from cutters. It’s grossstuff though so you may want to try soaking in some strong detergent mix and scrubbing with a brush. Works well on band saw blades too.

I use this knife dressing from bostik to decrease burning (aside from the technique recommendations from the others) It works great, and also make cleaning a lot easier. I also clean and dress with this before storing.. really aids the life of all your blades and knives.

I would toss it at this point, unless you have a small , flat diamond file / card, that will fit into the groove.If you do, be sure to make the same number of strokes on each flat side to maintain balance of the bit.